June 12, 2014 — Many HIV prevention campaigns in sub-Saharan Africa discourage young women from having sexual relations with older men, because older men are more likely to be infected with HIV than their younger counterparts. But surprisingly, a new Harvard School of Public Health (HSPH) study analyzing data on women in rural KwaZulu-Natal, South Africa — an area with a very high HIV infection rate — found partner age-disparity did not predict HIV infection among young women.

The paper was published online May 8, 2014 in the Journal of Acquired Immune Deficiency Syndromes (JAIDS) and will appear in the August print issue. Preliminary findings were presented earlier this year at the Conference on Retroviruses and Opportunistic Infections (CROI) in Boston.

“National policies on this topic in Africa have been built on the back of a limited evidence base. We hope that our analysis will spur further empirical investigation into whether this important null finding in a poor rural setting also holds true in other places, such as cities,” said lead author Guy Harling, postdoctoral research fellow in the Department of Global Health and Population (GHP) at HSPH.

Harling and his colleagues used data on almost 2,500 HIV-uninfected women enrolled in a longitudinal, population-based cohort in KwaZulu-Natal, established by the Africa Centre for Health and Population Studies. The women, ages 15 to 29, were followed for an average of almost three years, during which time 458 of them became infected with HIV.

The researchers suggest that despite the higher HIV prevalence in older men, their findings are plausible for several reasons. Young women may be more careful in choosing older partners and practice less-risky sex with older men. Additionally, young men are more likely to be recently infected and thus highly infectious, and older HIV-positive men are more likely to be taking antiretroviral drugs, reducing their risk of transmitting HIV.

“Campaigns warning women about the risks of sexual partnerships with older men may well provide social benefits, if they reduce unwanted pregnancies or school dropout. However, based on our study, such campaigns do not seem to be justified for HIV incidence reduction in settings similar to ours,” Till Bärnighausen, senior author and associate professor of global health at GHP, concluded.

Support for this study came from the Wellcome Trust and National Institutes of Health (NIH) grant R01 HD058482-01.